A system for conditioning air in an enclosure by directly contacting the air therein with a brine shower is disclosed in U.S. Pat. No. 4,355,683. In such system, air in an enclosure is contacted with a brine shower causing water vapor in the air to condense on the brine droplets thereby drying the air. The diluted brine so produced is reconstituted by first heating the diluted brine, and then spraying the heated diluted brine in a tower exposed to the atmosphere where the water extracted from the enclosure is evaporated into the atmosphere. The thus reconstituted brine is then returned to the brine shower associated with the enclosure, and the cycle repeats.
Condensation of water vapor on the brine droplets transfers to the droplets the heat of condensation of water thus increasing the sensible heat of the brine droplets. Normally, this heat is not recovered, particularly when a system as in the '683 patent is used.
In co-pending patent application Ser. No. 377,368 filed May 12, 1982 and Ser. No. 479,009 filed Mar. 23, 1983, a system is disclosed for storing this latent heat of condensation during one period of time (e.g., during the day when the enclosure is a greenhouse, and the water vapor is derived from the expiration of growing plants), and then releasing the stored heat to the enclosure during another period of time (e.g., during the night when the greenhouse is cool). This arrangement has the advantage of being very energy efficient.
In order for the system to operate properly and efficiently, the vapor pressure of the brine entering the shower must be less than the vapor pressure of the air in the greenhouse, this being the property of the brine that renders it hygroscopic and capable of efficiently drying the air in the enclosure. The vapor pressure of the brine is dependent on its temperature and concentration; two parameters that in large measure are established by the volume of brine in a reservoir that feeds the shower. Generally, a volume of about 0.4 m.sup.3 of brine, with a concentration of about 30% (calcium chloride or magnesium chloride), per square meter of greenhouse will be required in order to meet the above criterion. At today's prices, the cost of the brine alone will be about $40.00 per m.sup.2 of greenhouse. Compared with the cost of about $10.00 per m.sup.2 for constructing a greenhouse of plastic sheeting, it is clear that the cost of the brine is a dominant factor in the economics of greenhouse utilization. Reducing the amount of brine for cost purposes also reduces the expense of storage and transportation of the brine, and is advantageous in many instances. But, a reduction in the amount of brine will result in a significant increase in the temperature of the brine when it is contacted with the air in the enclosure. As the temperature of the brine increases so does its vapor pressure thus reducing the efficiency of the brine shower in drying the air in the enclosure. As a consequence, the conventional approach has involved providing a brine reservoir of sufficient volume that the heat added to the brine by the condensation of water vapor on the brine droplets in the shower does not significantly raise the temperature of the brine.
It is therefore an object of the present invention to provide a new and improved heat exchanger for removing the heat of condensation from brine.